An important consideration of industrial plant designers wherein the industrial plants uses a cooling systems having a cooling tower is the temperature of the condensate. In such industrial plants e.g. power plants, by decreasing the condenser temperature, the turbine exhaust pressure is able to be decreased, and therefore the output of the power plant is able to be increased.
Many power plants that are not accessible to an abundant supply of natural cooling water rely on cooling towers to provide their cooling needs. In a typical circulation circuit involving a cooling tower, the cooling water (CW) flows through a condenser, in which it is heated due to the condensation of turbine exhaust, is then injected to a cooling tower for recooling, and is finally pumped back to the condenser. The CW introduced into the cooling tower is cooled by an upwardly flowing draft of air, primarily through evaporative cooling, and is then collected in an underlying reservoir, which will be referred to hereinafter as a “basin”.
Since heat exchange in a cooling tower is accomplished by the evaporation of a portion of the CW, such that the latent heat of vaporization in the remaining portion of the CW required to cause the phase change is removed while providing the cooling effect, a supply of make-up water is needed to supplement the amount of water lost due to evaporation.
During the course of a hot summer day, the temperature of the water in the basin steadily increases as a result of the increased temperature of the ambient air. Likewise the temperature of the make-up water also increases as it is introduced into the basin and is mixed with the water. Due to this temperature increase, the condenser temperature is also increased, and therefore the output of the power plant is decreased. Consequently, the efficiency of the cooling system decreases.
Another important consideration of a cooling water supply system is the quality of the CW. As a result of CW evaporation from the cooling tower, dissolved solids such as calcium and magnesium salts, polymerized and non-polymerized silica as well as ions such as chlorides (and others depending on the water quality) are left behind. During the course of the day when more water evaporates, the concentration of dissolved solids and ions increases. If the concentration becomes excessive, scale and corrosion could form on surfaces of the cooling tower and of other components of the cooling water supply system, reducing heat transfer and adding maintenance costs to the system.
The accepted way of preventing the occurrence of an excessive concentration of dissolved solids and ions is by blowdown, whereby a portion of the CW together with dissolved solids and ions is continuously extracted from the basin and wasted. The extracted water is replaced by relatively clean make-up water to reduce the concentration of dissolved solids and ions while maintaining a substantially constant water level within the basin. In order to maintain a substantially constant water level within the basin, the blowdown pump adapted to extract dissolved solids and ions within the CW and the make-up pump for delivering the make-up water are operated in order to maintain a constant level in the basin. When using manual control, the risk of poor control of the supply of makeup water, supplied by the make up pumps, and extracting blow down, extracted by blow down pumps, all day long, including the hot hours, is greater such that the chance that make up well pumps as well as blow down pumps operate inaccurately so that scaling may result increases.
It is an object of the present invention to provide a cooling water supply system that minimizes increase of the condenser temperature during the hot summer months.
It is an additional object of the present invention to provide a cost effective cooling water supply system.
It is yet another object of the present invention to provide a cooling water supply system that increases the longevity of the blowdown pump and the make-up pump, relative to prior art systems.
It is yet a further object of the present invention to provide a cooling water supply system that is more effective in saving water than prior art systems.
Other objects and advantages of the invention will become apparent as the description proceeds.